Application of statistical and analytical treatments in the explanation the origin of groundwater chemistry. Case of the Messaad Plateau. South Algerian Steppe Region.

Abstract

The study area (Messaad plateau) is one of the arid areas with annual precipitation of the order of 150 mm. This area includes the Barremian aquifer, which plays a very important role in the supply of drinking water and irrigation water in the study area. The objective of this work is to study the origin of groundwater chemistry in the Barremian aquifer. The results obtained from the study of the physico-chemical parameters showed that the waters are very strongly mineralized overall, with a predominance of calcium sulphate facies and calcium chloride facies. Examination of the maps of the spatial variation of the various physico-chemical parameters reveals a high degree of mineralization in the South and South-East part of the study area near Oued Messaad. Statistical treatment by the application of the Principal Component Analysis (PCA) has shown that the increase in mineralization is mainly due to the dissolution of evaporative mineral-rich salt-bearing formations, and the predominant redox mechanism over that of acid hydrolysis in the acquisition of ions in groundwater. The hydro-chemical model based on Artificial Neuron Networks (ANN) of the multilayer perceptron (MLP) type has shown that the SO42-,Cl-,Ca2+,Na+ ions are the most important factors influencing the electrical conductivity of water. Analysis of the ionic ratios shows that these ions are the result of the dissolution of gypsum and halite continuously in the clays and marls of the Barremian formations.